Conventional approaches to measuring flow downhole in geothermal or engineered geothermal system (EGS) wellbores can be through the use of mechanical spinner tools, which makes use of a rotating paddle suspended and lowered (or raised) through the wellbore on a cable. But, such tools are notorious for failing, especially at high flow rates and at high temperatures, often due to mechanical failure and/or damage that occurs when lowering the mechanical spinner tool into a well. Likewise, non-uniformities in wellbore diameter can make calculating actual flow rate based on spinner rate data difficult and greatly complicate spinner-tool data interpretation. Further, spinner tools can be incapable of quantifying two-phase fluid flow (gas and liquid flow) within geothermal wellbores.
Radioactive tracers have been used to measure the success of hydraulic stimulations and characterize fracture properties such as surface area and volumes in petroleum wells. In a typical tracer test, the tracers, such as radioactively tagged proppant sands, can be introduced to a newly created fracture near the end of each phase of the stimulation process. Subsequent gamma logging can determine the location and relative importance of fractures created at each phase. Since such approaches involve the use of radioactive tracers, they can be expensive and potentially hazardous, especially to the environment. Likewise, such approaches use proppants, which are not commonly used in the hydraulic stimulation of geothermal or EGS reservoirs.